Hypothalamic LHRH levels play a critical role in triggering the ovulatory LH surge. We propose to define the fluctuation of hypothalamic LHRH degrading enzyme activity during the course of the rat estrus cycle. These observations will be correlated with simultaneously determined levels of hypothalamic LHRH as well as serum estradiol, progesterone, LH and FSH. LHRH degrading arylamidase enzymes may be capable of functioning as a fine tune mechanism in controlling hypothalamic LHRH levels. If is known that hypothalamic LHRH levels are elevated prior to and depressed subsequent to the proestrus LH surge; however, whether a change in the activity of LHRH degrading enzymes is associated with these fluctuations is unknown. Modulators of hypothalamic degrading enzyme activity will be sought by determining the effects of LH alone and combination with steroid (estradiol, progesterone and testosterone) pretreatment on the activity of the hypothalamic enzyme. A second mechanism possibly controlling hypothalamic LHRH levels is an alteration of the release rate. This possibility will be investigated by utilization of an in vitro perifusion system at selected time points along the estrus cycle. In order to characterize the enzyme activity, fractionation procedures will be used to ascertain if the total enzyme activity from a given enzyme source is separable into more than one physically and kinetically individual peak (isozymes) as well as to determine if the enzyme activity from different sources (hypothalamus, pituitary and serum) is kinetically as well as physically dissimilar. Elution from sieve columns will be used to estimate the molecular weight of the enzyme. Cell culture of intact, isolated hypothalamic and pituitary cells will be used to determine the direct effects of steroids and LH on degrading enzyme activity as well as to determine the biological activity of 125I-LHRH. Attempts will be made to work out an assay procedure for degrading enzymes utilizing 3H-LHRH as substrate. Success will depend on developing a relatively rapid method of estimating intact LHRH.